Giáo trình sản xuất sữa, dairy handbook, milk production,bao bì, tiếng anh chuyên ngành công nghệ thực phẩm.
PRIMARY PRODUCTION OF MILK Page of 18 Tetra Pak Dairy Processing Handbook PRIMARY PRODUCTION OF MILK ESSENTIAL FOOD FOR A GROWING WORLD Milk is a complex food that contains vital nutrients for the bodies of young mammals Milk is the only food of the mammal during the first period of its life and the substances in milk provide energy and antibodies that help protect against infection For humans, milk and dairy products make a significant contribution to meeting our bodies’ needs for calcium, magnesium, selenium, riboflavin, vitamin B12 and pantothenic acid (vitamin B5) and therefore play a key role in our development THE ORIGINS OF MILK PRODUCTION Today’s dairy animals are the product of thousands of years of breeding of untamed animals that lived at different altitudes and latitudes, at times exposed to severe and extreme weather conditions The techniques used in the production of milk using cows, goats, sheep and buffaloes began around six thousand years ago The same species of animals are kept for milking today These herbivorous animals were the natural choice to satisfy humans’ need for food and clothing as they are less dangerous and easier to handle than carnivorous animals The animals used for milk production are ruminants that eat quickly, in great quantities, and later digest their food Today, the most widespread milking animal in the world is the cow The cow can be found on all continents around the world Other animals commonly used in both subsistence and industrial dairy farming are goats, sheep and buffaloes The milk of these animals is of great importance to rural communities as a source of high-quality protein and other constituents Sheep and goats are of exceptional importance in areas such as the Mediterranean and in large areas of Africa and Asia The number of sheep and goats in the world is in the billions and they are the most numerous of all milk- and meat-producing animals The contribution of sheep and goats to milk and meat production in the poorest areas is also considerable: Both animals are a cheap source of food and are mainly kept in conditions where climatic, topographical, economic, technical or sociological factors limit the development of more sophisticated protein production systems THE NUTRITIONAL QUALITIES OF MILK Among the essential minerals and vitamins in milk are iron and vitamin D They are, however, not present in sufficient amounts, or in optimum proportions, to fulfil the requirements for complete nutrition During the first period of its life, the young animal therefore makes up for the shortage of certain nutrients in milk by exploiting the reserves it receives from its mother at birth, which are normally sufficient until its diet includes other foods To make the nutrients easily consumable and digestible, they are available in a liquid state, partly as a solution, partly as dispersion or suspension There is a wide variation in the balance of components in milk from various mammals, although the components themselves are basically the same Quantities of the various main constituents of raw milk from cows can vary considerably; between cows of different breeds and between individual cows of the same breed Water is the principal constituent and it is the carrier of all other components Cows’ milk consists of around 87 % water and 13 % dry substance that is suspended or dissolved in the water Besides ‘total solids’, the term solids non-fat is used in discussing milk composition http://www.dairyprocessinghandbook.com/print/chapter/primary-production-milk 25/09/2015 PRIMARY PRODUCTION OF MILK Page of 18 Table 1.1 The composition of milk (g/100g) of different species: Species Water Fat Casein Lactose Ash Whey protein Cow 87.3 4.4 2.8 4.6 0.7 0.6 Buffalo 82.2 7.8 3.2 4.9 0.8 0.6 Sheep 82.0 7.6 3.9 4.8 0.9 0.7 Goat 86.7 4.5 2.6 4.4 0.8 0.6 Human 87.1 4.6 0.4 6.8 0.2 0.7 COWS Considerable changes have taken place in the genetic makeup of the Bos Taurus species since the cow was taken on as a service animal some six thousand years ago The most significant of these is that the modern lactating dairy cow has a much higher milk production than its calf needs Genetic development has resulted in vastly increased lactation production Today’s cows produce roughly six times as much as primitive cows Even around thirty years ago a cow would typically only produce somewhere in the region of 4.000 kilograms of milk per calf, whereas today’s cows yield an average of between 7.000 and 12.000 kilograms of milk Some cows can produce up to 14.000 litres of milk or more per calf Increased knowledge about the importance of herd management, animal well-being and optimized feeding has contributed to this genetic development Fig 1.0 As is the case with all mammals, cows produce milk for their offspring Therefore, the production of milk is closely linked to the reproductive cycle Before a female cow can start to produce milk she must first have had a calf Females reach sexual maturity at the age of seven or eight months and are then called heifers Heifers are usually mated when they are 15-18 months old by either ‘natural service’ using a bull or via artificial insemination The gestation period typically lasts 265-300 days and heifers tend to give birth to their first calves at the age of 2-2.5 years old They are typically bred again four to eight weeks after calving SECRETION AND THE LACTATION PERIOD Milk is secreted in the cow’s udder – a hemispherical organ divided into right and left halves by a crease Each half is divided into quarters by a shallower transverse crease Each quarter has one teat with its own separate mammary gland It is therefore theoretically possible to get milk of four different qualities from the same cow A sectional view of the udder is shown in Figure 1.1 The cow’s udder is composed of glandular tissue containing milk-producing cells The external layer of this tissue is muscular, thus giving cohesion to the body of the udder and protecting it against injury The glandular tissue contains around two billion tiny bladders called alveoli The milk-producing cells are located on the inner walls of the alveoli, which occur in groups of 8-120 Capillaries leading from the alveoli converge into progressively larger milk ducts which lead to a cavity above the teat This cavity, known as the cistern of the udder, can hold up to 30 % of the total milk in the udder The cistern of the udder has an extension reaching down into the teat; this is called the teat cistern At the end of the teat there is a channel 1-1.5 centimetres in length Between milking, the teat channel is closed by a sphincter muscle which prevents milk from leaking out and bacteria from entering the udder The whole udder is laced with blood and lymph vessels These bring nutrient-rich blood from the heart to the udder, where it is distributed by capillaries surrounding the alveoli In this way, the milk-producing cells are furnished with the necessary nutrients for the secretion of milk Spent blood is carried away by the capillaries to veins and returned to the heart Large quantities of blood flow through the udder A cow that produces 60 litres of milk per day will need some 30.000 litres of blood circulating through its mammary gland http://www.dairyprocessinghandbook.com/print/chapter/primary-production-milk 25/09/2015 PRIMARY PRODUCTION OF MILK Page of 18 As the alveoli secrete milk their internal pressure rises If the cow is not milked, secretion of milk stops when the pressure reaches a certain limit Increase of pressure forces a small quantity of milk out into the larger ducts and down into the cistern Most of the milk in the udder, however, is contained in the alveoli and the fine capillaries in the alveolar area These capillaries are so fine that milk cannot flow through them of its own accord It must be pressed out of the alveoli and through the capillaries into the larger ducts Muscle-like cells surrounding each alveolus perform this duty during milking (see Figure 1.2) Secretion of milk in a cow’s udder begins shortly before calving, so that the calf can begin to feed almost immediately after birth The cow then continues to give milk for around 10 months (approximately 305 days) This period is known as lactation During the lactation period, milk production gradually decreases and after 305 days it can drop to 25-50 % of its peak volume At this stage milking is discontinued and the cow has a non-lactating period of up to 60 days prior to calving again With the birth of the calf a new lactation cycle begins The udder also contains a lymphatic system It carries waste products away from the udder The lymph nodes serve as a filter that destroy foreign substances but also provide a source of lymphocytes to fight infections Sometimes, around parturition cows giving birth for the first-time suffer from oedema, partly caused by the presence of milk in the udder which compresses the lymph nodes Fig 1.1 A sectional view of the udder Fig 1.2 Squeezing of milk from alveolus Cistern of the udder Teat cistern Teat channel Alveolus COLOSTRUM Calves are born lacking their own immune protection as their immune system develops slowly In response, the first milk a cow produces after calving is called colostrum, which differs greatly from normal milk in both composition and nutritional properties Calves are dependent on receiving maternal antibodies and an essential supply of immunoglobulins via colostrum Antibodies are globular proteins produced by the body’s immune response system to fight diseases Each individual varies in its ability to produce antibodies and thus fight disease Animals receiving inadequate colostrum are extremely vulnerable to intestinal infection and subsequent scours A calf needs around 1.000 litres of milk for normal growth and that is the approximate quantity which the primitive cow produced for each calf To illustrate an individual cow’s milk production, milk yield is typically plot against time to get a lactation curve Yield will rise during the first months after calving, followed by a long period of continuous decline The shape of the lactation curve will differ from individual to individual and from breed to breed Feeding and management also influence the shape and have a significant impact on the total amount of milk produced Lactation is ideally 305 days, but in practice it is usually more, followed by a two-month dry period prior to the next calving MILKING During milking, the oxytocin hormone must be released into the cow’s bloodstream for the udder to empty This hormone is secreted and stored in the pituitary gland When the cow is prepared for milking by the correct stimuli, a http://www.dairyprocessinghandbook.com/print/chapter/primary-production-milk 25/09/2015 PRIMARY PRODUCTION OF MILK Page of 18 signal is sent to the gland, which then releases its store of oxytocin into the bloodstream In the primitive cow, the stimulus was provided by the calf’s attempts to suck on the teat The oxytocin was released when the cow feels the calf sucking A modern dairy cow normally has no calf present during milking so stimulation of the milk “let-down” is done by the preparation of milking, i.e the sounds, smells and sensations associated with milking time The oxytocin hormone begins to take effect about a minute after preparation has begun and causes the muscle-like cells to compress the alveoli This generates pressure in the udder and can be felt with the hand; it is known as the let-down reflex The pressure forces the milk down into the teat cistern, from which it is sucked into the teat cup of a milking machine or pressed out by the fingers during hand milking The effect of the let-down reflex gradually fades away as the oxytocin is diluted and decomposed in the bloodstream, disappearing after 5-8 minutes Milking should therefore be completed within this period of time If the milking procedure is prolonged in an attempt to “strip” the cow, unnecessary strain is placed on the udder and the cow becomes irritated and may be difficult to milk Milk fat consists mainly of triglycerides, which are synthesized from glyceroles and fatty acids Long-chained fatty acids are absorbed from the blood Short chained fatty acids are synthesized in the mammary gland from the components acetate and beta hydroxybutyrate which have their origins in the blood Milk protein is synthesized from amino acids also with origin from the blood and consists mainly of caseins and to a smaller extent whey proteins Lactose is synthesized from glucose and galactose within the milk-secreting cell Vitamins, minerals, salts and antibodies are transformed from the blood across the cell cytoplasm into the alveolar lumen MILKING FREQUENCY Due to labour patterns and working hours, milking twice a day has long been the common practice in industrial nations In countries where labour is inexpensive, more frequent milking is often practiced During the last few decades, focus has increasingly been put on milking more frequently, in particular in high-yielding herds There are many benefits associated with more-frequent milking Changing from milking twice a day to three times a day markedly increases milk production Published data shows that one additional milking can produce 5-25% more milk per cow per day In addition, lactation becomes more persistent and prolonged The reason why milk production increases with a more frequent milking could be a more frequent exposure of hormones stimulating milk secretion to the mammary gland However, as mentioned above, milk contains an inhibitor with negative feedback control on milk secretion More frequent removal of this inhibitor therefore results in higher production Cows with a small udder cistern are more sensitive to the frequency of milking Smaller the cisterns are more susceptible to frequent milk removal Frequent milking has both short- and long-term effects In the short term, milk production increases due to enhanced activity in the milk-secreting cells In the long term, production increases due to increased number of milk-secreting cells The latter indicates that it is possible to influence the number of milk-secreting cells during an established lactation, which is of importance to the milk producing capacity of the animal Among the most important benefits of more frequent milking is improved animal welfare It has been observed that high-yielding animals will typically not lie down for a few hours before milking Moreover, many high yielders are producing up to 60 kilograms of milk per day and are milked twice with 8-16 hour milking intervals These cows yield nearly 40 kilograms of milk during morning milking alone Cows with such high amounts of milk in the mammary gland are exposed to high udder pressure, which undoubtedly causes discomfort It has been observed that highyielding cows prefer to be milked more frequently than two or three times a day when they are given the choice MILKING TECHNIQUES TRADITIONAL MILKING BY HAND Milking continues to be done by hand as it has been for thousands of years on farms all around the world Cows on smallholder farms tend to be milked by the same people every day and become accustomed to their milker Letdown is stimulated by the familiar sounds of milking preparations The first squirts of liquid from the teats are normally rejected and then careful visual inspection of the first milk enables the milker to look for visible signs of the status of udder health Two opposing quarters of the udder are milked at a time: one hand presses the milk out of the teat cistern, after which the pressure is relaxed to allow more milk to run down from the udder cistern At the same time, milk is pressed out of the other teat In this way the two teats are milked alternately When two quarters have been emptied, the milker can proceed to milk the other two Milk is collected in pails and poured through a strainer to remove coarse impurities into a churn holding 30-50 litres The churns are then chilled to 4° C and stored before being transported to the dairy Immersion or spray chillers are commonly used for cooling http://www.dairyprocessinghandbook.com/print/chapter/primary-production-milk 25/09/2015 PRIMARY PRODUCTION OF MILK Page of 18 CONVENTIONAL MILKING SYSTEMS The basic principle of the milking machine is shown in Figure 1.3 The milking machine extracts the milk from the teat by vacuum A vacuum pump, a vacuum vessel, a vessel for collecting milk, teat cups and a pulsator are all essential parts of the milking machine The teat cup unit consists of a cup containing an inner tube of rubber, called the teat cup liner The inside of the liner, in contact with the teat, is subjected to a constant vacuum of about 50 kPa (50 % vacuum) during milking The pressure in the pulsation chamber (between the liner and teat cup) is regularly alternated by the pulsator between 50 kPa during the suction phase and atmospheric pressure during the massage phase The result is that milk is sucked from the teat cistern during the suction phase During the massage phase, the teat cup liner is pressed together allowing a period of teat massage This is followed by another suction phase, and so on as shown in Figure 1.4 Relief of the teat during the massage phase is necessary to avoid accumulation of blood and fluid in the teat Such congestion in the teat can be painful to the cow, and milk let down and milking performance can be affected Repeated congestion at successive milking sessions can even have an influence on the udder health The pulsator alternates between suction and massage phases about 50-60 times per minute The four teat cups, attached to a manifold called the milk claw, are held on the cow’s teats by suction and the friction between the teat and the teat cup liner Vacuum is alternately (alternate pulsation) applied to the left and right teats or, in some instances, to the front teats and rear teats The applying of vacuum to all four teats at the same time (simultaneous pulsation) is less common The milk is drawn from the teats directly to the milk pail or via a vacuum transport pipe to a receiver unit An automatic shut-off valve operates to prevent dirt from being drawn into the system if a teat cup should fall off during milking After the cow has been milked, the milk pail is taken to a milk room where it is emptied into a churn or a special milk tank for cooling To eliminate the heavy and time-consuming work of carrying filled pails to the milk room, a pipeline system may be installed for direct transport of the milk to the milk room (Figure 1.5) Such systems are most common today It allows milk to be conveyed in a closed system straight from the cow to a collecting tank in the milk room This is a considerable advantage in terms of ensuring proper hygiene Regardless if the milking system is of bucket, pipeline or automatic type it is important that it is designed to prevent air leakage during milking Excessive air leakage can influence the quality of the milk and cause elevated levels of free fatty acids The machine milking plant is also provided with Cleaning-In-Place facilities Fig 1.3 Machine milking equipment Fig 1.4 The phases of machine milking a Teat cup liner Fig 1.5 General design of pipeline milking system Vacuum pump Vacuum pipeline Milk cooling tank Milk pipeline AUTOMATIC MILKING SYSTEMS Milking is one of the most labour-intensive and time-consuming jobs in dairy farming In addition, milking has to take place at least twice a day all year around Automated milking systems (Figure 1.6) are one solution to this problem as they offer dairy farmers with large herds reduced labour requirements, higher milk quality, improved animal http://www.dairyprocessinghandbook.com/print/chapter/primary-production-milk 25/09/2015 PRIMARY PRODUCTION OF MILK Page of 18 health and increased yield In contrast to conventional milking, in which people bring the cows to be milked, automatic milking places emphasis on the cow’s inclination to be milked in a self-service manner several times a day Figure 1.8 shows a typical dairy farm layout including an automatic milking system When the cow wants to be milked, she walks to the milking station A transponder on the cow identifies it, and if the cow was milked recently, she is directed back to the resting or feeding area The cow enters the automatic milking station and an individual amount of concentrate is served In an automatic milking system (or “voluntary milking system”) teats are detected by lasers and a vision camera As an example, the teats can be cleaned separately by means of a teat-cup-like device (Figure 1.7), using tepid water applied intermittently at a certain pressure and turbulence to ensure efficient cleaning Drying of the teats is carried out by compressed air in the same teat-cup Pre-milking is carried out by the cleaning teat-cup, which applies vacuum at the end of the cleaning cycle The cleaning teat-cups are finally flushed with water Sensors detect whether or not pre-milking has been carried out and fore-milking applied for a few seconds to ensure that sufficient milk is evacuated and the let-down reflex is activated Teat cups are automatically attached sequentially and milk from the four teats is kept separate until the milk meter records the amount from each quarter Spraying each individual teat with disinfectant is the final stage of automatic milking http://www.dairyprocessinghandbook.com/print/chapter/primary-production-milk 25/09/2015 PRIMARY PRODUCTION OF MILK Fig 1.6 The heart of an automatic milking system The cow goes when she wants into the milking station where the teats are cleaned and milked Fig 1.7 Teat-cup for cleaning, drying and pre-milking The teat is flushed with tepid water for cleaning and finally dried with air The pre-milk goes together with cleaning water to drain Page of 18 Fig 1.8 The layout of a modern dairy farm with an automatic milking system Automatic milking station Control room Milk cooling and storage Smart gate for preselecting the cows attempting the milking station Living area Feeding station Calf section MILK QUALITY AND ANIMAL HEALTH Cows are normally productive for around three lactations A prerequisite to produce milk in an economical way is to have a relatively high yield with high quality for as long as the farmers plans for keeping the animal and avoiding http://www.dairyprocessinghandbook.com/print/chapter/primary-production-milk 25/09/2015 CLEANING OF DAIRY EQUIPMENT Page 10 of 13 Fig 21.5 Principle of the centralized CIP system Cleaning unit (within the broken line) Tank for alkaline detergent Tank for acid detergent Plate heat exchanger Object to be cleaned: • A Milk treatment • B Silo tanks • C Tank gardens • D Filling machines Water and detergent solutions are pumped from storage tanks in the central station to various CIP circuits The detergent solutions and hot water are kept hot in insulated tanks The required temperatures are maintained by heat exchangers The final rinse water is collected in a rinse-water tank and used as pre-rinsing water in the next cleaning program The milk/water mixture from the first rinsing water is collected in a rinse-milk tank The detergent solutions must be discharged when they have become dirty after repeated use The storage tank must then be cleaned and refilled with fresh solutions It is also important to empty and clean the water tanks, especially the rinse-water tank, at regular intervals to avoid the risk of infecting an otherwise clean process line An example of the design of a central CIP station is illustrated in Figure 21.6 A station of this type is usually highly automated The tanks have electrodes for high and low level monitoring Returning of the cleaning solutions is controlled by conductivity transmitters The conductivity is proportional to the concentrations normally used at dairy cleaning At the phase of flushing with water, the concentration of detergent solution becomes lower and lower At a pre-set value, a change-over valve routes the liquid into the drain, instead of the relevant detergent tank CIP programs are controlled from a computerized sequence controller Large CIP stations can be equipped with multiple tanks to provide the necessary capacity Fig 21.6 A common tank garden can supply several CIP stations (A to F) with detergent, water and other solutions http://www.dairyprocessinghandbook.com/print/chapter/cleaning-dairy-equipment 25/09/2015 CLEANING OF DAIRY EQUIPMENT Page 11 of 13 DECENTRALIZED CIP Decentralized CIP is an attractive alternative for large dairies, where the distance between a centrally located CIP station and peripheral CIP circuits would be extremely long The large CIP station is replaced by a number of smaller units located close to the various groups of process equipment in the dairy Figure 21.7 illustrates the principle of a decentralized CIP system, also called a satellite CIP system Fig 21.7 Decentralized CIP system Storage tank for alkaline detergent Storage tank for acid detergent Ring lines for detergents Objects to be cleaned Decentralized CIP units Decentralized CIP system with its own detergent tanks This still has a central station for storage of the alkaline and acid detergents, which are individually distributed to the individual CIP units in main lines Supply and heating of rinsing water (and detergent, when required) are arranged locally at the satellite stations, one of which is shown in Figure 21.8 http://www.dairyprocessinghandbook.com/print/chapter/cleaning-dairy-equipment 25/09/2015 CLEANING OF DAIRY EQUIPMENT Page 12 of 13 Fig 21.8 CIP unit Heat exchanger Pressure pump Dosing pumps These stations operate on the principle that the various stages of the cleaning program are carried out with a carefully measured minimum volume of liquid – just enough to fill the circuit to be cleaned A powerful circulation pump is used to force the detergent through the circuit at a high flow rate The principle of circulating small batches of cleaning solutions has many advantages Water and steam consumption, both momentary and total, can be greatly reduced Milk residues from the first rinse are obtained in a more concentrated form and are therefore easier to handle and cheaper to evaporate Decentralized CIP reduces the load on sewage systems as compared to centralized CIP, which uses large volumes of liquid The concept of single-use detergents has been introduced in conjunction with decentralized CIP, as opposed to the standard practice of detergent recycling in centralized systems The one-time concept is based on the assumption that the composition of the detergent solution can be optimized for a certain circuit The solution is considered spent after having been used once In some cases, however, it may be used for pre-rinsing in a subsequent program VERIFYING THE CLEANING EFFECT Verification of the effect of cleaning must be regarded as an essential part of cleaning operations It can take two forms: visual and bacteriological inspection Because of the advance of automation, process lines today are seldom accessible for visual inspection This must be replaced by bacteriological monitoring, concentrated to a number of strategic points in the line CIP results are usually checked by cultivating coliform bacteria When a swab test of a http://www.dairyprocessinghandbook.com/print/chapter/cleaning-dairy-equipment 25/09/2015 CLEANING OF DAIRY EQUIPMENT Page 13 of 13 surface is made, the criterion is less than one coli bacterium per 100 cm2 of the checked surface The result is unacceptable if the count is higher These tests can be made on the surfaces of the equipment after completion of the CIP program This applies to tanks and pipe systems, especially when excessively high bacteria counts have been detected in the products Samples are often taken from the final rinse water or from the first product that passes through the line after cleaning All products must be checked for bacteriological quality in their packages to obtain full quality control of the manufacturing process The complete quality control program, in addition to the coliform test, also includes determination of the total count of microorganisms and organoleptic control (tasting) Source URL: http://www.dairyprocessinghandbook.com/chapter/cleaning-dairy-equipment http://www.dairyprocessinghandbook.com/print/chapter/cleaning-dairy-equipment 25/09/2015 DAIRY EFFLUENT Page of Tetra Pak Dairy Processing Handbook DAIRY EFFLUENT Water used in domestic and industrial applications can become polluted to varying degrees Water is also used as a transport medium to carry away waste products As awareness of the importance of improved standards of water treatment grows, process requirements become increasingly exacting The food industry contributes significantly to pollution, particularly as the pollutants are of organic origin Organic pollutants normally consist of 1/3 dissolved, 1/3 colloidal and 1/3 suspended substances, while inorganic materials are usually present mainly in solution ORGANIC POLLUTANTS The normal way to express the concentration of a pollutant is to specify the total quantity per unit volume of sewage Another, more modern way of analysing the presence and quantities of organic substances in sewage effluent is the use of chromatography, such as High-Performance Liquid Chromatography (HPLC) However, the quantity of organic substances is normally determined in the form of • Biological oxygen demand (BOD) • Chemical oxygen demand (COD) • Calcining loss • Total organic carbon (TOC) BIOLOGICAL OXYGEN DEMAND (BOD) BOD is a measure of the content of biologically degradable substances in sewage The substances are broken down by microorganisms in the presence of (and therefore with consumption of) oxygen Oxygen demand is measured in terms of the quantity of oxygen consumed by microorganisms over a period of five days (BOD5) or seven days (BOD7), in decomposing the organic pollutants in waste water at a temperature of 20 °C BOD is measured in mg oxygen/l or g oxygen/m3 The following relationship is assumed for municipal sewage: BOD7 = 1.15 x BOD5 BOD is a measure of the content of biologically degradable substances in sewage CHEMICAL OXYGEN DEMAND (COD) COD indicates the quantity of the pollutants in waste water that can be oxidized by a chemical oxidant The normal reagents used for this purpose are strongly acid solutions (to ensure complete oxidation) of potassium dichromate or potassium permanganate at high temperature Consumption of oxidant provides a measure of the content of organic substance and is converted to a corresponding quantity of oxygen, expressing the result as mg oxygen/l or g oxygen/m3 The COD/BOD ratio indicates how biologically degradable the effluent is Low values, i.e < 2, indicate relatively easily degradable substances, while high values indicate the contrary However, this relationship cannot be used generally, but a typical value of COD/BOD for municipal sewage effluent is often < In the FIL-IDF Bulletin about Dairy Effluents, Document 138, 1981, reported (Doedens) that the COD/BOD5 ratio for effluent generated in different groups of dairies producing liquid milk, butter or cheese ranged from 1.16 to 1.57, at http://www.dairyprocessinghandbook.com/print/chapter/dairy-effluent 25/09/2015 DAIRY EFFLUENT Page of an average of 1.45 In other groups of dairy plants producing milk powder, whey powder, lactose and casein, the ratio varied from 1.67 to 2.34, with an average of 2.14 However, the general conclusion of the FIL-IDF Bulletin was that a COD:BOD ratio established in one dairy plant could not be transferred with sufficient reliability to another plant COD indicates the quantity of the pollutants in waste water that can be oxidized by a chemical oxidant CALCINING LOSS Calcining loss is obtained by first determining the dry solids content in a sample, and then calcining it so that the organic substance is burnt The difference in weight before and after calcining represents the quantity of organic substance The value is expressed as a percentage TOTAL ORGANIC CARBON (TOC) TOC is another measure of the quantity of organic materials, determined by measuring the quantity of carbon dioxide produced from combustion of a sample The unit is mg/l DRINKING WATER The table below is extracted from Guidelines for drinking-water quality, 2nd ed Vol Health criteria and other supporting information, 1996 Geneva, World Health Organization (WHO) In WHO's Guidelines for drinking-water quality, also a large number of microbiological and other chemical parameters affecting the water quality can be found Drinking water The table below is extracted from Guidelines for drinking-water quality, 2nd ed Vol Health criteria and other supporting information, 1996 Geneva, World Health Organization (WHO) In WHO's Guidelines for drinking-water quality, also a large number of microbiological and other chemical parameters affecting the water quality can be found Table 22.1 Guideline values for drinking-water quality Element value Abbr Guideline mg/l Cadmium Cd < 0.003 Arsenic As < 0.01 Chromium Cr < 0.05 Lead Pb < 0.01 Mercury Hg < 0.001 INORGANIC POLLUTANTS The inorganic components of sewage consist almost entirely of salts, and are determined largely by the ionic composition and salt concentration in the mains water The presence of these salts in sewage is normally http://www.dairyprocessinghandbook.com/print/chapter/dairy-effluent 25/09/2015 DAIRY EFFLUENT Page of unimportant Present-day effluent treatment processes concentrate on the reduction of nitrogen, phosphorus salts and heavy metals Nitrogen and phosphorus compounds are important, as they are nutrients for organisms, e.g algae, in recipients As a result of the growth of algae, secondary processes can proceed in the recipient, forming further organic substances which, when they decompose, can result in considerably higher oxygen demand than is caused by primary organic pollutants in the sewage effluent Heavy metals may be toxic in high concentrations and may disturb the ecosystems also in low concentrations DAIRY WASTE WATER Dairy waste water can be divided into three categories: Cooling water Sanitary waste water Industrial waste water COOLING WATER As cooling water is normally free from pollutants, it is discharged into the storm water piping system, the system for run-off water from rain and melting snow, etc SANITARY WASTE WATER The sanitary waste water is normally piped direct to the sewage treatment plant with or without first having being mixed with industrial waste water INDUSTRIAL WASTE WATER Industrial waste water emanates from spillage of milk and products thereof, and from cleaning of equipment that has been in contact with milk products The concentration and composition of the waste depends on the production programme, operating methods and the design of the processing plant Sewage treatment plants are dimensioned to treat a certain quantity of organic substances and also to be able to deal with certain peak loads However, one organic substance – fat – presents particularly difficult problems Besides having a high BOD (cream with 40 % fat has a BOD5 of about 400,000 mg oxygen/l while skim milk has 70,000 mg/l), fat sticks to the walls of the mains system, as well as causing sedimentation problems in the sedimentation tank as it rises to the surface Dairy waste water should therefore pass a flotation plant where it is aerated with “dispersion water” (the method of supplying finely-dispersed air bubbles to the water at a pressure of 400 – 600 kPa is called dissolved-air flotation) The air bubbles attach themselves to the fat, carrying it rapidly to the surface where it is strained off, manually or mechanically depending on the size of the plant The flotation plant is often located close to the dairy building and the waste passes through it in a continuous flow The defatted effluent can then be mixed with the sanitary waste water going to the sewage treatment plant Table 22.2 lists the BOD of some milk products http://www.dairyprocessinghandbook.com/print/chapter/dairy-effluent 25/09/2015 DAIRY EFFLUENT Page of Table 22.2 BOD of some milk products BOD5 mg/ l Product BOD7 mg/ l Cream 40% fat 400 000 450 000 Whole milk 4% fat 120 000 135 000 Skim milk 0.05% fat 70 000 80 000 Whey 0.05% fat 40 000 45 000 Whey conc 60% DM 400 000 450 000 PH OF DAIRY EFFLUENT The pH of dairy effluent varies between and 12, as a result of the use of acid and alkaline detergents for plant cleaning Both low and high pH values interfere with the activity of the microorganisms that break down organic pollutants in the biological treatment stage of the sewage treatment plant, transforming them into biological sludge (cell detritus) As a rule, waste water with a pH of over 10 or below 6.5 must not be discharged to the sewage system, as it is liable to corrode the pipes Used detergents are therefore normally collected in a mixing tank, often located close to the cleaning plant, and the pH is measured and regulated to about pH 7.0 before it is discharged to the drain Waste water with a pH of over 10 or below 6.5 must not be discharged to the sewage system Table 22.3 Guideline values for advanced treated sewage water Outlet in river/lake Outlet in sea Outlet in municipal WWTP Ammonia-nitrogen, mg/l 1–5 < 10 < 100 Total-nitrogen, mg/l < 25 10 – 15 80 – 100 Total-phosphorus, mg/l 0.3 – 0.5 0.5 – 1.5 10 – 30 BOD7, mg/l O2 10 – 15 15 – 20 500 – 2000 pH 6–9 – 10 > 6.5 Grease, mg/l